The long-term goal of the project is to better understand how diverse oral bacteria modulate phosphate concentrations near the tooth interface. This likely has a significant influence on the balance of oral health in children and adults. This project proposes a new and previously unrecognized mechanism of phosphate modulation in the oral cavity. This project will investigate how specific bacteria in the oral environment can accumulate external free orthophosphate to internally synthesize and store long chains of phosphate as polyphosphate (poly-P). This process has the potential to create undersaturated conditions at the tooth interface and accelerate subsurface tooth demineralization (tooth decay) under acidic conditions. Bacteria that accumulate poly-P may also, under specific conditions, release their internally stored phosphate, into the external environment leading to ion oversaturation, which may have a protective role. Our group has determined through genomic screening and direct evidence, that the majority of species associated with acute dental decay have the ability to accumulate poly-P. This project will investigate how the diverse microbiome in the oral cavity contains these specific phosphate-accumulating bacteria that are modulating phosphate ions within the biofilm. In this project, we will: 1) identity, quantify, and localize the oral bacterial species capable of polyphosphate-accumulation that are found in carious lesions; 2) determine to what degree these phosphate-accumulating bacteria mediate mineral dissolution and/or re- precipitation; and 3) determine which conditions mediate polyphosphate accumulation and extracellular phosphate release in different oral bacteria species. The novelty of this work is rooted in the remarkable past discoveries of the oral human microbiome. Our project will explore how a diverse class of bacteria within the oral microbiome may not possess the classic virulence-related factors, but play a significant and active role in dissolution via the ion exchange pathway specifically via phosphate accumulation and release. This unrecognized mechanism is likely a key aspect of maintaining oral hard tissue health and preventing and managing dental cavities in children and adults.